Stack Testing Methods

Stack Testing Methods

Stack Testing Methods

Whether for engineering purposes or for compliance with EPA regulations, source emissions testing — or stack testing — is an important part of a facility’s operations.

When conducting your stack test the methods used to conduct the testing must be understood and followed carefully, in order to obtain reliably accurate data that will be accepted by the EPA to show compliance.  These methods have been set by the EPA, and are available for public review on the EPA website, which has been linked at the bottom of this article.

A full understanding of each and every method is a long and difficult process that will often require the assistance of specifically trained engineers such as can be found in an experienced stack testing organization.

However, it is helpful to have a basic understanding of some of the more common types of stack testing methods, and for that purpose we have compiled a short list of commonly analyzed pollutants, and the EPA-approved methods used to test for them.

Particulate Matter (PM): EPA Methods 5, 201a, 202 – Particulate matter, also known as particle pollution or PM, is a complex mixture of extremely small particles and liquid droplets. PM is made up of a number of components, including acids (such as nitrates and sulfates), organic chemicals, metals, and soil or dust particles.  Particulates are categorized by size.  “Inhalable coarse particles,” such as those found near roadways and dusty industries, are larger than 2.5 micrometers and smaller than 10 micrometers in diameter. “Fine particles,” such as those found in smoke and haze, are 2.5 micrometers in diameter and smaller.  The smaller the particles the more hazardous they are, as they are more easily absorbed.

  • Method 5 is used to determine filterable particulate matter. The PM mass, which includes any material that condenses at or above the filtration temperature (248 +25oF) is determined gravimetrically.
  • Method 201a is used to measure filterable particulate matter (PM) emissions equal to or less than a nominal aerodynamic diameter of 10 micrometers (PM10) and 2.5 micrometers (PM2.5). You cannot use this method on a wet source.
  • Method 202 is used to measure condensable particulate matter. Method 5 and 201a only measure particulate matter that condenses at or above 248oF. Method 202 is used in conjunction with the above methods to account for PM emissions that condense below 248oF.

Gaseous Emissions (SO2, NOx, CO): EPA methods 3a, 6c, 7e and 10 – This is a catch-all term for a variety of air pollutants that are emitted in gaseous form.  The most common, according to the EPA, are:

  • Carbon monoxide (CO): EPA method 10 — A colorless, odorless gas emitted from combustion processes.  Particularly in urban areas, the majority of CO emissions to ambient air come from mobile sources.
  • Nitrogen dioxide (NO2): EPA method 7e — One of a group of highly reactive gasses known as nitrogen oxides (NOx), also including nitrous acid and nitric acid. NO2 forms quickly from emissions from vehicles, power plants, and off-road equipment. It contributes to ground-level ozone, and fine particle pollution.
  • Sulfur dioxide (SO2): EPA method 6c — One of a group of highly reactive gasses known as “oxides of sulfur.”  The largest sources of SO2 emissions are from fossil fuel combustion at power plants (73%) and other industrial facilities (20%).  Smaller sources of SO2 emissions include industrial processes such as extracting metal from ore, and the burning of high sulfur containing fuels by locomotives, large ships, and non-road equipment.

Each of these methods uses a continuous instrumental analyzer to determine emissions, and requires mobile laboratories or access to climate controlled shelters. Real time results using these methods are available on a ppmvd basis.

Multiple Metals (As, Be, Cd, Cr, Pb, Hg, Ni): EPA Method 29 – This method can be used to determine emissions of 17 different metals, including mercury. Method 5 can be run in the same train to determine filterable particulate emission at the same time. Metals are found naturally in the environment, but also in manufactured products.  The most commonly tested metals include Lead, Mercury, and Arsenic.

Special Note on CEMS RATA: Many facilities use a system know as a CEMS, or Continuous Emissions Monitoring System, that provides continuous feedback on emission levels and act as a substitute for regular stack testing.  These CEMS units are subject to a 3rd party check known as a Relative Accuracy Test Audit, or RATA, to guarantee that it is reading emission levels accurately.   (See info on CEMS Testing)

For how to conduct the methods themselves, there is information available on the EPA website, in an index format, at the following webpage:

We invite you to contact Environmental Source Samplers (ESS) to learn more about our stack testing services.  Visit or call 888-363-0039.

Brian Mellor About Brian Mellor

Brian Mellor works with Environmental Source Samplers, Inc. (ESS), an environmental consulting firm specializing in stack testing, CEMS Testing, and EPA air emissions compliance.

ESS has conducted international stack testing projects at Johnson Atoll, in the Philippines, the Dominican Republic, Hong Kong, and various parts of Europe. If you need a team that will do your international job with efficiency and effectiveness, call ESS at (910) 799-1055 or visit

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